× 4. Mauritius. (Viewed in Two Directions.) (_F.C. Coll._) ] ANTHOZOA.--The true Corals have a stony skeleton, and this is capable of easy preservation as a fossil. There is hardly any fossiliferous stratum of importance which has not its representative corals. In Australia their remains are especially abundant in the Silurian, Devonian (Fig. 33), and Carboniferous formations, and again in the Oligocene and Miocene. SPONGES.--The framework of the sponge may consist either of flinty, calcareous, or horny material (Fig. 34). The two former kinds are well represented in our Australian rocks, the first appearing in the Lower Ordovician associated with graptolites, and again in the Cretaceous and Tertiary rocks (Fig. 35); whilst the calcareous sponges are found in Silurian strata, near Yass, and again in the Cainozoic beds of Flinders, Curlewis and Mornington in Victoria. [Illustration: =Fig. 35.= =Spicules of a Siliceous Sponge (Ecionema newberyi, McCoy sp.)= Highly magnified. Cainozoic Shell-Marl. Altona Bay Coal-Shaft.] [Illustration: =Fig. 36.= =Nummulites (N. gizehensis Ehr. var. champollioni, de la Harpe).= About nat. size. Middle Eocene Limestone. Cyrene, Northern Africa. (_Coll. by Dr. J. W. Gregory_). ] PROTOZOA.--The important and widely-distributed group of the Foraminifera ("hole-bearers") belonging to the lowest phylum, the Protozoa, generally possess a calcareous shell. The tests range in size from tiny specks of the fiftieth of an inch in diameter, to the giant Nummulite, equalling a five shilling piece in size (Fig. 36). Their varied and beautiful forms are very attractive, but their great interest lies in their multifarious distribution in all kinds of sediments: they are also of importance because certain of the more complex forms indicate distinct life zones, being restricted to particular strata occurring in widely-separated areas. [Illustration: =Fig. 37.--Siliceous Skeletons of Radiolaria.= × 58. Late Cainozoic Age. Bissex Hill, Barbados, West Indies. (_F.C. Coll._) ] Members of the allied order of the Radiolaria have a flinty shell (Fig. 37); and these organisms are often found building up siliceous rocks such as cherts (Fig. 38). PLANTS.--The harder portions of plants which are found in the fossil state are,--the wood, the coarser vascular (vessel-bearing) tissue of the leaves, and the harder parts of fruits and seeds. Fossil wood is of frequent occurrence in Palaeozoic, Mesozoic and Cainozoic strata in Australia, as, for instance, the wood of the trees called _Araucarioxylon_ and _Dadoxylon_ in the Coal measures of New South Wales (see _antea_, Fig. 3). [Illustration: =Fig. 38.--Radiolaria in Siliceous Limestone.= × 40. Middle Devonian: Tamworth, New South Wales. (_From Prof. David's Collection_). ]